Automation framework for online review of daily dose distributions using CT on Rails in proton therapy

To demonstrate a framework for calculating daily dose distributions for proton therapy in a timeframe amenable to online evaluation using CT-on-Rails.

Tasks associated with calculation of daily dose are fully automated. A rigid registration between daily and planning images is used to propagate beams and targets for calculation of daily dose; additionally, risk structures are propagated using deformable registration to facilitate online evaluation. An end-to-end constancy test was carried out using a pelvis phantom containing a simulated target and bladder contour. 97 Daily fan-beam CT data sets associated with 10 clinical patients were processed to demonstrate feasibility and utility of online evaluation. Computing times and dosimetric differences are reported.

The phantom constancy test took 62 s to complete with no notable discrepancies in the registrations or calculated dose. Max doses were identical for target and bladder contours on initial and repeat scans (359 and 310 cGy (RBE) respectively). Total processing time for 97 daily patient images averaged 154.6 s (73.0 - 222.0 s; SD = 31.8 s). On average, dose calculation accounted for 35 % of total processing time. Average differences in D95 for target contours was 1.5 % (SD = 1.6 %) with a max decrease of 5.9 % on a single daily image.

Daily dose can be automatically calculated in a timeframe amenable to online evaluation using scanner utilities in conjunction with the scripting API of a commercial treatment planning system. Online evaluation of dose in proton therapy is useful to detect clinically relevant changes, guide setup, and facilitate treatment or replanning decisions.